Single-stroke pneumatic apparatus

ABSTRACT

A single-stroke pneumatic apparatus incorporates a hollow cylindrical frame1) with inlet and outlet ports (2,3). A handgrip (4) containing a directional flow control (5) is attached to the upper end of the frame. A striker (6) is provided in the bore of the frame (1) with provision for reciprocating back and forth so as to divide this bore into a forward-stroke chamber (8) a back-stroke chamber (7). A tool (9) is supported in the lower end of the frame (1). A shell (10) with holes (11) surrounds the frame (1) from the outside, forming a muffling chamber (12) therewith, within a full length of the stroke of the striker (6). Additional outlet ports (15) are provided in the lower end of the frame (1) which communicate the back-stroke chamber (8) with the muffling chamber (12) located wherein is a filter (6) overlapping the holes (11) in the shell (10).

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to pneumatic apparatus of the percussivetype used in construction, mining, mechanical engineering and metallurgyand has specific reference to single-stroke pneumatic apparatus.

Description of the Prior Art

Single-stroke pneumatic apparatus commonly employed for marking,centre-pricking, marking-off and chiselling off risers are pneumatichammers. The tool the hammer is fitted with varies with the application.It can be a stamp, a prick-punch, a hobby or a chisel. The tool issupported in a hollow frame with inlet and outlet ports and a strikerdividing the frame bore into forward- and working-stroke chambers. Adirectional flow control is provided on the frame. The source of energyis compressed air fed from a mobile or stationary compressor over aflexible hose. In operation, the compressed air admitted into thechambers of the frame with the aid of the directional flow controlmanipulated by the operator, causes the striker to reciprocate back andforth axially and deliver cyclewise blows at the end face of the tool.The work done by the tool materializes in any of the followingoperations depending on the type of the tool: marking, centre-pricking,chiselling or riveting.

The atmosphere at the working place where pneumatic hammers are in useis commonly laden with dust and the operator cannot but stay in such asurrounding. Therefore, the problem of increasing the reliability of thepneumatic hammer is one of great concern.

Known in the art is a single-stroke pneumatic apparatus (cf. USSRInventor's Certificate No. 781048, IPC B25D 9/14, 1980) comprising ahollow cylindrical frame provided with inlet and outlet ports, and astriker recurrently interacting with a resilient means located at an endface of the frame. The directional flow control is a solenoid-actuatedvalve operated by a microswitch. The valve made up of three partslacking a mechanical link with each other is of intricate design. Apartfrom that, the known apparatus lacks reliability, for dust and otherfine particles are sucked into the bore of the frame through the outletports when the striker is on a back stroke. The noisy high-velocityexhaust from the apparatus creates trying labour conditions for theoperator.

Also known is a single-stroke pneumatic apparatus, i.e. a pneumatichammer (cf. German Patent No. 671,958, Cl. 87b 2/11, 1939) comprising ahollow cylindrical frame with inlet and outlet ports, a spring-loadedstriker forming forward- and back-stroke chambers in the frame bore, ahandgrip located wherein is a directional flow control and a tool fixedin the upper end of the frame.

In the known apparatus, the outlet ports are laid out in a way whichcannot prevent ingress of dust-laden atmosphere into the frame bore.Therefore, the hammer cannot last long. The noisy exhaust from theapparatus creates trying labour conditions for the operator.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a single-stroke pneumaticapparatus, in which an enhanced reliability and improvements in theservice conditions thereof would be ensured by the design of theair-distribution means.

The invention includes a single-stroke pneumatic apparatus comprising ahollow cylindrical frame with inlet and outlet ports, a handgripattached to the upper end of the frame, a directional flow controllocated in the handgrip and used to admit compressed gaseous fluidrecurrently into the bore of the frame, a striker located in the bore ofthe frame with provision for reciprocating back and forth so as todivide the bore of the frame into a forward-stroke chamber--admittedrecurrently through the inlet ports is compressed gaseous fluid--and aback-stroke chamber, a return spring fitted to the striker at that endthereof which faces the back-stroke chamber, a tool attached to thelower end of the frame, and a shell with holes which surrounds the frameand forms therewith a muffling chamber communicating with the atmospherevia the holes in the shell and with the back-stroke chamber via theoutlet ports. According to the invention the shell extends through afull length of stroke of the striker, the frame is provided at its lowerend with additional outlet ports which connect the back-stroke chamberto the muffling chamber and a filter is provided in the muffling chamberwhich overlays the holes in the shell--located on a level therewith--andserves as a muffler when the stroker displaces towards its lowermostposition.

The apparatus of the above design is protected against an ingress ofdust and other fine particles into the bore of the frame and thereforelasts longer than any known prior art devices. It also effectivelymuffles the noise in operation, creating satisfactory labour conditions,owing to the presence of the filter through which gaseous fluid isexhausted.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a shematic sectional elevation of a single-stroke pneumaticapparatus according to the invention which illustrates the arrangementof parts at the instant of delivering a blow at the tool; and

FIG. 2 is a shematic sectional elevation of the apparatus at the instantof a back stroke (the striker is in its topmost position).

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a single-stroke pneumatic apparatuscomprises ahollow cylindrical frame 1 with inlet and outlet ports 2, 3.A handgrip 4 is immovably attached to the upper end of the frame 1. Adirectional flow control 5 is contained inside the handgrip 4. A striker6 is provided in the bore of the frame 1 with provision forreciprocating back and forth soas to divide the bore of the frame 1 intoa forward stroke chamber 7 and a back-stroke chamber 8, and a tool 9 isattached to the lower end of the frame 1. An immovable shell 10 withholes 11 surrounds the frame 1 from the outside all through the lengthof the striker stroke and forms in the frame a muffling chamber 12 whichcommunicates with the atmosphere via theholes 11 in the shell 10 andwith the back-stroke chamber 8 via the outlet ports 3. Mounted in thebore of the frame 1 on the side of the back-strokechamber 8 are a returnspring 13 cooperating with the striker 6 and a shock-absorbing stop 14.Additional outlet ports 15 are provided in the lower end of the frame 1which connect the back-stroke chamber 8 to the muffling chamber 12, anda filter 16 is provided in the muffling chamber 12 on a level with theholes 11.

The apparatus operates in the following manner.

Compressed gaseous fluid is admitted into the forward-stroke chamber 7via a union in the handgrip 4 (FIG. 1) the directional flow control 5and the inlet ports 2 when a trigger 17 is being depressed (FIG. 1). Atthe said time, the back-stroke chamber 8 is connected to the atmospherevia the outlet ports 3, the additional outlet ports 15, the mufflingchamber 12, the filter 16 and the holes 11. The striker 6 is acted uponby the compressed gaseous fluid in the forward-stroke chamber 7 travelsdownwardsagainst the action of the return spring 13, whereby the gaseousfluid contained in the back-stroke chamber is expelled into the mufflingchamber12 through the additional outlet ports 15 and hence into theatmosphere viathe filter 16 and the holes 11. As soon as the top edge ofthe travelling striker 6 uncovers the outlet ports 3, the gaseous fluidcontained in the forward-stroke chamber 7 escapes into the atmospherethrough the outlet ports 3, the filter 16 and the holes 11. At thisstage, the filter 16 functions as the muffler. Continuing on the downstroke, the striker 6 delivers a blow at the end face of the tool 9 incontact with the work, causing it to do the job. The outlet ports 3relieve the striker 6, and consequently the tool 9, of a continuingpressure which may cause the tool9 to bounce, losing contact with thework. The flow section and number of the outlet ports 3 should beselected so that the pressure buildup in the forward-stroke chamber 7 ishigher than the maximum force of the compressed return spring 13.Otherwise the apparatus will not function.

When the trigger 17 is released, no compressed gaseous filud enters theforward stroke chamber 7 and this becomes connected to the atmospherevia the outlet ports 2 and the directional flow control 5. As thestriker 6 isreturned into the topmost position due to the action of thereturn spring 13, air is sucked into the back-stroke chamber 8 throughthe holes 11, thefilter 16, the muffling chamber 12 and the additionaloutlet ports 15. The filter 16 separates dust from the air, keeping thedust outside the back-stroke chamber 8.

The disclosed apparatus compares favourably with the known single-strokepneumatic apparatus in that it prevents ingress of dust and other fineparticles inside the frame and operates at a significantly lower noiselevel.

These advantages add 10-15% to the apparatus' reliability and improvelabour conditions.

The invention can be used to advantage in coping with such jobs asmarking and marking-off, centre-pricking, riveting and chiselling offrisers.

It may also be of utility in trimming roofs of mine openings, punchingholes, breaking concrete and other civil engineering applications.

What is claimed is:
 1. A single-stroke pneumatic apparatus comprising ahollow cylindrical frame (1) with inlet and outlet ports (2,3), in anupper end of which frame a handgrip (4) is fixed, accommodating adirectional air control (5) for periodic admission of a compressedgaseous medium into a bore (1) in the frame, in which bore a striker (6)is disposed with provision for recirprocation, said striker dividingsaid bore into a forward-stroke chamber, periodically communicated viathe inlet ports (2) with the compressed gaseous medium, and aback-stroke chamber (8), and a tool (9) mounted in a lower end of theframe (1), on which frame a shell (10) with holes (11) is arranged, saidshell forming with the frame (1) a muffling chamber (12), communicatingthrough the holes (11) in the shell (10) with the atmosphere and throughthe outlet ports (3) with the back-stroke chamber (8), from whichchamber the striker (6) is spring-loaded with respect to the frame (1),characterized in that the shell (10) is provided all through the lengthof the stroke of the striker (6), and in that additional outlet ports(15) are provided in the lower end of the frame (1), communicating theback-stroke chamber (8) with the muffling chamber (12), in which chamber(12) a filter (16) is disposed level with the holes (11) in the shell(10), said filter (16) overlapping said holes (11) and acting as amuffler as the striker (6) travels to its lower-cost position.